This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We proposed experiments that test hypotheses about the neural mechanisms that underlie the brain's ability to make decisions. Our experiments address the mechanism used by the brain to convert sensory information represented by neurons in the visual cortex to a decision about what this information means for purposes of planning behavior. We showed that neurons in the association cortex of the macaque represent the accumulation of this evidence for one choice and against an alternative. This year, we demonstrated that the mechanism that explains choice and decision time also applies when the environment controls the availability of evidence. The surprising finding is that the brain acts as it would in a choice-reaction time experiment. It terminates the decision when ready despite the availability of addition information (Kiani et al, 2008). We have also completed a study of the mechanism to decision-making when there are more than 2 options (Churchland et al, 2008). Several theoretical studies performed in collaboration with investigators outside the WaNPRC were completed this year (Wong et al, 2008;Beck et al, 2008;Ganguli et al, 2008). Decision-making bridges the gap between sensation and behavior. Nearly all non-reflexive behaviors require the brain to draw upon its sensory cortex to guide future behavior. Thus, the neural mechanisms for the simple decisions we study are likely to lend insight into more complex cognitive strategies. Our experiments ultimately furnish new insights into the causes and treatments of mental disorders affecting perception, planning and reasoning.